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PDF AAT1236 Data sheet ( Hoja de datos )
| Número de pieza | AAT1236 | |
| Descripción | High Efficiency White LED Drivers | |
| Fabricantes | Skyworks Solutions | |
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DATA SHEET
AAT1236
High Efficiency White LED Drivers for Backlight and Keypad
General Description
The AAT1236 is a highly integrated, high efficiency power
solution for white LED and keypad backlights in mobile/
portable devices. It is based on a switching boost con-
verter which steps up the single cell lithium-ion/polymer
battery voltage to drive 5 strings of series-connected
white LEDs with precision current regulation. The AAT1236
is capable of driving a total of four LEDs per channel.
The boost converter can produce an output drive of up
to 24V at 100mA. The high switching frequency (up to
2MHz) provides fast response to load transients and
allows the use of small external components. A fully
integrated control circuit simplifies the design and reduc-
es total solution size.
A two-wire I2C serial digital interface is used to individu-
ally turn each output sink on/off and adjust the LED cur-
rent by group. Unlike conventional pulse width modula-
tion (PWM) control of LED brightness, the AAT1236 drives
the LEDs with constant, non-pulsating current. The inter-
face is fully compliant to the Fast/Standard mode I2C
specification, allowing a transfer rate of up to 400kHz.
A similar device is also available with a proprietary
Advanced Simple Serial Control™ (AS2Cwire™) single
wire interface; please see the AAT1235 datasheet.
The AAT1236 is available in a Pb-free, thermally-enhanced
16-pin 3x4mm TDFN package and is specified for opera-
tion over the -40°C to +85°C temperature range.
Typical Application
L=2.2µH
D1
Features
• Input Supply Voltage Range: 2.7V to 5.5V
• Maximum Boost Output Drive: Up to 24V at 100mA
• Up to 85% Efficient Operation
• Up to 2MHz Switching Frequency with Small Inductor
• User-Programmable Full-Scale LED Current, Up to
30mA
• Two-Wire, I2C Compliant Serial Interface
▪ Two Addressable Registers
• Independent LED Current Control by Group
▪ Backlight Group B1-B2, 16 Settings
▪ Auxiliary Group A1-A3, 16 Settings
• Independent LED ON/OFF Control
▪ Fast, 400kHz Serial Transfer Rate
• Non-Pulsating, High-Performance LED Current Drive
for Uniform Illumination
▪ 10% Absolute Accuracy
▪ 2% Channel-to-Channel Matching
• Over-Voltage and Over-Temperature Protection
• Automatic Soft-Start Minimizes Large Inrush Current
at Startup
• Available in 3x4mm TDFN34-16 Package
Applications
• Digital Still Cameras (DSCs)
• Keypad Backlight
• Large Panel Displays
• Mobile Handsets
• PDAs and Notebook PCs
• Personal Media Players
• White LED Backlight
Up to 24V max
Keypad or
RGB LEDs
COUT
2.2µF
Input :
2.7V~5.5V
CIN
2.2µF
LIN
VIN
IN
Enable
I2C
Interface
SDA
SCL
Backlight
LEDs
SW B 1 B 2 A 1 A 2 A 3
AAT1236
OV
EN SDA SCL
RSET GND AGND
R1
22.6kΩ
R2
187kΩ
R3
12.1kΩ
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202111A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
1
1 page  
DATA SHEET
AAT1236
High Efficiency White LED Drivers for Backlight and Keypad
I2C Interface Timing Details
SDA
SCL
TLOW
TSU_DAT
THD_STA
THD_DAT
THIGH
TSU_STA
THD_STA
TSU_STO
TBUF
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202111A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
5
5 Page 
DATA SHEET
AAT1236
High Efficiency White LED Drivers for Backlight and Keypad
Under light load conditions, the inductor OFF interval
current goes below zero and the boost converter enters
discontinuous mode operation. Further reduction in the
load current results in a corresponding reduction in the
switching frequency. The AAT1236 provides pulsed fre-
quency operation which reduces switching losses and
maintains high efficiency under light load conditions.
Operating frequency varies with changes in the input volt-
age, output voltage, and inductor size. Once the boost
converter has reached continuous mode, further increas-
es in the LED current will not significantly change the
operating frequency. A small 2.2µH (±20%) inductor is
selected to maintain high frequency switching (up to
2MHz) and high efficiency operation for outputs up to
24V.
Soft Start / Enable
The input disconnect switch is activated when a valid
supply voltage is present and the EN/SET pin is strobed
high. Slew rate control on the input disconnect switch
ensures minimal inrush current as the output voltage is
charged to the input voltage, prior to switching of the
N-channel power MOSFET. A monotonic turn-on is guar-
anteed by the built-in soft-start circuitry, which elimi-
nates output current overshoot across the full input
voltage range and over all load conditions.
Current Limit and
Over-Temperature Protection
The switching of the N-channel MOSFET terminates when
a current limit of 1.5A (typical) is exceeded. This mini-
mizes power dissipation and component stresses under
overload and short-circuit conditions. Switching resumes
when the current decays below the current limit.
Thermal protection disables the AAT1236 when internal
power dissipation becomes excessive, as it disables both
MOSFETs. The junction over-temperature threshold is
140°C with 15°C of temperature hysteresis. The output
voltage automatically recovers when the over-tempera-
ture fault condition is removed.
Over-Voltage Protection
Over-voltage protection prevents damage to the AAT1236
during open-circuit on any LED channel causing high
output voltage conditions. An over-voltage event is
defined as a condition where the voltage on the OV pin
exceeds the over-voltage threshold limit (VOV = 1.2V
typical). When the voltage on the OV pin has reached
the threshold limit, the converter stops switching and
the output voltage decays. Switching resumes when the
voltage on the OV pin drops below the lower hysteresis
limit, maintaining an average output voltage between
the upper and lower OV thresholds multiplied by the
resistor divider scaling factor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN input.
Under-voltage lockout (UVLO) guarantees sufficient VIN
bias and proper operation of all internal circuitry prior to
soft start.
I2C Serial Interface and Programmability
The current sink magnitude of each group and the on/off
status of each channel is controlled via an I2C serial
interface. I2C is a widely used interface which requires a
master to initiate all the communications with the
device. I2C protocol consists of two active wire SDA
(serial data line) and SCL (serial clock line). Both wires
are open drain and require an external pull-up resistor
to VCC. The SDA pin serves the I/O function, and the SCL
pin controls and references the I2C bus. The I2C protocol
is a bidirectional bus which allows both read and write
actions to take place; the AAT1236 supports the write
protocol only. Since the protocol has a dedicated bit for
Read or Write (R/W), when communicating with the
AAT1236, this bit must be set to “0.”
I2C Programming Register
Address and Register Data
After sending the device address, the I2C master should
send an 8-bit register address and 8-bit data for pro-
gramming. The AAT1236 has two registers; the
Brightness Control Register determines the percentage
of the maximum current set by RSET applied to each
channel and the Channel Control Register determines
which channels are enabled or disabled. The program-
ming is as follows:
BR_CRTL – LED Brightness Control Register
(Address: 00h)
BR_CTRL D7 D6 D5 D4 D3 D2 D1 D0
Bit name BX3 BX2 BX1 BX0 AX3 AX2 AX1 AX0
Control register BR_CRTL can be used to control LED
brightness for each group. Control bits BX3, BX2, BX1,
BX0 set the percentage of the maximum LED level in
Group B. Control bits AX3, AX2, AX1, AX0 set the per-
centage of the maximum LED level in Group A.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202111A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet AAT1236.PDF ] | |
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